PROJECT SUMMARY Metastatic progression of the primary tumor accounts for the majority of cancer deaths. While the initial steps of the metastatic cascade are rather well defined, identification of targets to block this process remains a major clinical challenge. Previous studies have elegantly investigated the mechanistic contribution of tumor cell intrinsic properties that promote metastasis in bladder urothelial carcinomas. However, the functional significance of the tumor microenvironment and its contribution to this complicated process is not well characterized, and therefore, warrants investigation. The long-term goal of this renewal application is to continue explore how collagens?a major extracellular matrix component of the microenvironment?act as a ligand to mediate crosstalk with their receptor on tumor cells to facilitate the metastatic cascade. We will investigate the downstream regulatory mechanisms of collagen receptor signaling in both the primary tumor and metastatic sites, and to exploit these regulatory processes as a revolutionizing approach to target metastases. Such innovative approaches to perturb collagen-cancer crosstalk?not only at the primary tumor but also at the metastatic niche?will move the field forward by providing a new conception in metastatic disease management, and likely extend beyond bladder carcinomas to other cancer types.